The acid secreting cell of the gastric mucosa undergoes a remarkable transition as it is simulated to secrete HCl, electrically, morphologically, and biochemically. It is planned to investigate the electrical events at either surface of the Necturus oxyntic cell by patch clamp methods, using cell attached, excised patch and whole cell recording to monitor channels and membrane expansion that is associated with activation of secretin. Electron microscopy, using acid space dependent probes, will be used in isolated intact of permeable rabbit gastric glands to determine the site of activation of the HK ATPase, and the pathway of retrieval of the enzyme following inhibition of the secretion by receptor antagonists. Intact and permeable parietal cells and derived vesicles will be used to evaluate the changes that must occur in carriers and pumps at either side of the parietal cell in the process of activating acid secretion. With these methods, a model will be derived that integrates the electrophysiology, morphology, and biochemical of the membrane processes involved in the transition from rest to secretion.